The present invention relates to a process for manufacturing potato fibers and to potato fibers manufactured in the process.
Potatoes are a natural product which, in addition to being an important staple food, also are the raw material for manufacturing starch and alcohol. In conventional manufacture of starch from potatoes, the by-products potato pulp, potato juice and potato water are obtained besides starch. The potato juice is the liquid content of the potatoes, and the potato water is diluted potato juice obtained in the starch manufacturing process. The potato pulp is the fiber mass and part of the potato juice, usually about 20%, and normally has a total solids content (TS) of about 13-15%.
In starch manufacture, starch is the desired main product, and potato juice and potato pump are by-products which cannot simply be passed to waste since they can cause waste disposal and environmental problems. A further problem are the large amounts of potato juice and potato pulp. Up to now, the by-products have been taken care of in that potato juice is used as fertiliser and potato pulp as cattle wet fodder. However, this solution cannot be considered optimal since the starch manufacturer's costs for getting rid of the potato pulp are unfavourably related to the profit obtainable. Moreover, potato pulp is rather difficult to handle because of its highly viscous and sticky nature.
As will be appreciated, it would be a great step forward if one could provide a process for refining potato pulp to a product which is more readily handled and does not cause waste disposal or environmental problems and also has a higher economic value.
A quite different problem is that, in recent years, it has been found that people in general are eating improper food in the sense that the content of food fibers is too low. Nutrionists and hygienists therefore recommend a substantially increased intake of fibers. Such increased intake can be achieved either by choosing particularly fiber-rich foodstuffs or by adding food fibers to ordinary foodstuffs so as to increase their content of food fibers. To the last-mentioned purpose, attempts have been made with varying success at manufacturing different kinds of food fibers based on plants, for use in foodstuffs. In this context, it has been difficult to manufacture food fibers which are neutral in taste, i.e. which have no undesired taste of the plant from which they originate, or because of the manufacturing process. Consequently, the food industry is in need of food fibers which are neutral in taste and which can be used as a fiber addition in foodstuffs.
SUMMARY OF THE INVENTION
The object of the present invention is to try and solve or reduce the above-mentioned problems and thus eliminate the waste disposal and environmental problems connected with potato pulp, and to provide a refined, economically valuable product which can be readily handled and used as a food fiber addition in foodstuffs, neutral in taste.
This object is achieved according to the invention in that dried potato fibers are manufactured from potato pulp in the manner defined in the appended claims and the description below.
The process according to the invention comprises the following steps:
(a) washing potatoes, PA0 (b) dividing the potatoes into potato juice, starch and pulp, PA0 (c) separating the starch from the potato juice and the pulp, characterised in that PA0 (d) solid impurities are removed from the pulp, the potato juice being defoamed and added to the pulp to form a pulp/potato juice mixture which is relieved of solid impurities by density separation, whereupon PA0 (e) the pulp is dewatered to remove part of the potato juice, and PA0 (f) the dewatered pulp is refined such that the content of potato juice and dissolved salts in the pulp is reduced in that the pulp is prepressed to a dry solids content of 20-30% and then washed by adding water to obtain a dry solids content of 11-16%, whereupon the pulp is finally pressed to a dry solids content of 20-30%, after which the refined pulp is subjected to PA0 (g) drying and PA0 (h) grinding to the final potato fiber product.
The potato fibers manufactured in the process according to the invention are characterised in that they have a particle size of not more than 1 mm, contain not more than about 15% by weight of protein, not more than about 15% by weight of starch, and that the remainder consists of lignin and polysaccharides other than starch.
It has been found that the potato fibers manufactured according to the invention seem to bring further unexpected and favourable effects besides the advantages as a fiber addition in foodstuffs, which is neutral in taste. The isolation of the potato cell wall substance according to the present invention renders it possible to utilise the substances (cellulose, hemicelluloses, lignin and pectin substances) which occur naturally in potatoes. These substances can have positive effects on diseases such as piglet diarrhoea which is a very serious and frequently fatal disease. It has also been convincingly shown that, in diabetics, pectin substances and hemicelluloses give a flattened blood sugar curve and result in a reduced need for insulin.
The potato fiber product obtained according to the present invention consists of particles comprising cell fragments of the walls of the potato tissue. The particles contain not more than about 15% by weight, preferably not more than about 10% by weight of starch, and not more than about 15% by weight, preferably not more than about 10% by weight of protein, the balance being cellulose-containing cell residues. These fragments represent a porous network with a plurality of cavities and pores. Some fragments contain residual starch grains around which proteins are enriched. The cavities and pores each take up and bind water, and thee properties are highly developed in potato fibers. The total fiber volume determines first of all the water absorbing capacity. In their dry state, the particles are very compact, but when water is added, the particles swell rapidly and are separated into a number of smaller and highly swollen particles. The potato fibers can be admixed as a binder and stabiliser to food products to increase the fiber content, which is advantageous from the viewpoint of nutrition. The fiber swelling degree and the particle size influence the water-retaining capacity and the consistency of the final product. The average particle size of the potato fibers according to the invention is not more than about 1 mm, preferably about 0.5 mm. By average particle size is meant the diameter of a circle, the surface of which is as large as the average projected surface of the potato fiber.